Natural substances are known to contain components useful as drugs, such as anticancer agents and many drugs have been thus far developed from natural substances. Typical examples of anticancer agents derived from natural substances developed in recent years and now clinically put into practical use include irinotecan hydrochloride (CPT-11) semi-synthesized from camptothecin, which is an extracted alkaloid from Camptotheca trees from china, taxotere (TXT) semi-synthesized from extracts of the needles of Western yew trees (Taxus brevifolia), taxol (TXL) isolated from extracts of the bark of Pacific yew trees, etc.
The anticancer agents derived from natural substances like the anticancer agents whose active components are synthetic compounds, are strongly injurious (or toxic) to cancer cells thus they have also strong affects on normal cells, and may induce severe side effects, resulting in many cases in abandonment of the therapy by medication.
Also, in the midway of the therapy by medication, there arises in many clinical sites a problem of drug tolerance that cancer cells acquire in which the drug or other plural drugs will become no longer effective. This is a great hindrance to the therapy by medication.
On the other hand, Chinese medicine formulae prepared by blending a plurality of galenicals containing many active components have advantages in that they exhibit gentle and sustained effects and that they hardly cause side effects and drug tolerance. However, since they can give no sufficient effects, there have been substantially no cases in which they are used for the purpose of treating cancers.
Under the circumstances, there exists a possibility that search on natural substances of animal and plant origin will result in finding ones including active anticancer components. Actually, many such approaches have been proposed in patent information, academic literature, etc.
However, the conventional methods in which an anticancer component alone is isolated and purified or semi-synthesized from a particular natural substance as a therapeutic drug cannot solve the problems of side effects and drug tolerance, which are the biggest problems of cancer therapy. So far as the organism recognizes an anticancer agent as a foreign matter containing a cytotoxic factor, the problems of side effects and drug tolerance cannot be avoided to occur. Furthermore, other problems on anticancer agents derived from natural substances include one that in many cases the component found with difficulty is poor as a resource, so that its industrial application is impossible.